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copied!<p>Here are some examples using <code>data.table</code>. I'm using the functions defined in the previous answers.</p> <pre><code>my.summary <- function(x, na.rm=TRUE){ result <- c(Mean=mean(x, na.rm=na.rm), SD=sd(x, na.rm=na.rm), Median=median(x, na.rm=na.rm), Min=min(x, na.rm=na.rm), Max=max(x, na.rm=na.rm), N=length(x)) } set.seed(123) df <- data.frame(id = 1:1000, Distance = rnorm(1000, 50, 100), Age = rnorm(1000, 50, 100), Height = rnorm(1000, 50, 100) ) df$Coning <- as.factor(ifelse(df$Distance > 0, "Yes", "No")) library(fBasics) library(data.table) DT <- data.table(df) setkey(DT, id) </code></pre> <p>Group by factor variable "Coning"</p> <pre><code>DT[,lapply(.SD,my.summary),by="Coning"] </code></pre> <p>Using <strong>my.summary() and basicStats()</strong> Just numeric Variables</p> <pre><code>DT[,lapply(.SD, my.summary),, .SDcols = names(DT)[2:4]] BS <- DT[,sapply(.SD, basicStats),, .SDcols = names(DT)[2:4]] BS[, summary := znames] setnames(BS, 1:3, names(DT)[2:4]) BS DT[,lapply(.SD, summary),, .SDcols = names(DT)[2:4]] </code></pre> <p>using <strong>summary()</strong> Numeric Variable using</p> <pre><code>DT[,sapply(.SD, function(x) if(is.numeric(x)) summary(x)),, .SDcols = names(DT)[2:4]] </code></pre> <p>Factor Variable</p> <pre><code>DT[,sapply(.SD, function(x) if(is.factor(x)) summary(x)),, .SDcols = names(DT)[5]] </code></pre> <p>Using the quantile function is also quite useful:</p> <pre><code>DT[,sapply(.SD, function(x) if(is.numeric(x)) quantile(x)),, .SDcols = names(DT)[2:4]] </code></pre>

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